Inspection of a lithographic mask that is protected by a pellicle

ABSTRACT

A system and a method for evaluating a lithography mask, the system may include: (a) electron optics for directing primary electrons towards a pellicle that is positioned between the electron optics and the lithography mask; wherein the primary electrons exhibit an energy level that allows the primary electrons to pass through the pellicle and to impinge on the lithographic mask; (b) at least one detector for detecting detected emitted electrons and for generating detection signals; wherein detected emitted electrons are generated as a result of an impingement of the primary electrons on the lithographic mask; and (c) a processor for processing the detection signals to provide information about the lithography mask.

BACKGROUND OF THE INVENTION

Extreme ultra violet (EUV) lithographic masks are used during themanufacturing process of semiconductor wafers and other modernelectrical components. Defects of EUV lithographic masks are duplicatedon multiple electrical components and thus are very costly. In order toprotect EUV lithographic masks these masks are usually covered (orplaced below) by pellicles.

EUV lithographic masks should be inspected in order to detect defects.The detection typically includes scanning the EUV lithographic maskswith low energy electrons and detecting these low energy electrons.

It has been found that some modern pellicles prevent (or at leastdramatically reduce) the passage of low energy electrons through thepellicles and thus prevent inspection of EUV lithographic masks that areprotected by pellicles.

There is a growing need to inspect EUV lithographic masks that areprotected by pellicles.

SUMMARY

According to an aspect of the invention, there are provided a method anda system for inspecting EUV lithographic masks that are protected bypellicles. According to an embodiment of the invention, the methodcomprises: directing by electron optics, primary electrons towards apellicle that is positioned between the electron optics and thelithography mask; wherein the primary electrons exhibit an energy levelthat allows the primary electrons to pass through the pellicle and toimpinge on the lithographic mask; detecting, by at least one detector,detected emitted electrons and generating detection signals; whereindetected emitted electrons are generated as a result of an impingementof the primary electrons on the lithographic mask; and processing, by aprocessor, the detection signals to provide information about thelithography mask.

According to another embodiment of the invention, there is provided asystem for evaluating lithography mask, the system comprises: electronoptics for directing primary electrons towards a pellicle that ispositioned between the electron optics and the lithography mask; whereinthe primary electrons exhibit an energy level that allows the primaryelectrons to pass through the pellicle and to impinge on thelithographic mask; at least one detector for detecting detected emittedelectrons and for generating detection signals; wherein detected emittedelectrons are generated as a result of an impingement of the primaryelectrons on the lithographic mask; and a processor for processing thedetection signals to provide information about the lithography mask.

According to another embodiment, there is provided a method forevaluating a lithographic mask, the method comprises: receivingdetection signals; wherein the detection signals are generated by atleast one detector that detects detected emitted electrons; wherein thedetected emitted electrons are generated as a result of directing byelectron optics, primary electrons towards a pellicle that is positionedbetween the electron optics and the lithography mask; wherein theprimary electrons exhibit an energy level that allows the primaryelectrons to pass through the pellicle and to impinge on thelithographic mask; and processing, by a processor, the detection signalsto provide information about the lithography mask.

According to yet another embodiment of the invention, there is provideda system for evaluating lithography mask, the system comprises: aninterface for receiving detection signals; wherein the detection signalsare generated by at least one detector that detects detected emittedelectrons; wherein the detected emitted electrons are generated as aresult of directing by electron optics, primary electrons towards apellicle that is positioned between the electron optics and thelithography mask; wherein the primary electrons exhibit an energy levelthat allows the primary electrons to pass through the pellicle and toimpinge on the lithographic mask; and a processor for processing thedetection signals to provide information about the lithography mask.

According to an embodiment of the invention, there is provided anon-transitory computer readable medium that stores instructions for:receiving detection signals; wherein the detection signals are generatedby at least one detector that detects detected emitted electrons;wherein the detected emitted electrons are generated as a result ofdirecting by electron optics, primary electrons towards a pellicle thatis positioned between the electron optics and a lithography mask;wherein the primary electrons exhibit an energy level that allows theprimary electrons to pass through the pellicle and to impinge on thelithographic mask; and processing the detection signals to provideinformation about the lithography mask.

According to various embodiments of the invention: the detected emittedelectrons can be backscattered electrons that are emitted from thelithographic mask; the detected emitted electrons may exclude secondaryelectrons emitted from the pellicle due to an interaction of the primaryelectrons with the pellicle; the detected emitted electrons may excludesecondary electrons emitted from the pellicle due to an interaction ofthe backscattered electrons with the pellicle; the detected emittedelectrons may exclude secondary electrons emitted from the pellicle dueto (a) an interaction of the primary electrons with the pellicle and dueto (b) an interaction of the backscattered electrons with the pellicle;the detected emitted electrons may be secondary electrons that areemitted from the pellicle due to an interaction of the backscatteredelectrons with the pellicle, wherein the backscattered electrons areemitted from the lithographic mask; the detected emitted electrons mayexclude electrons emitted from the pellicle due to an interaction of theprimary electrons with the pellicle; the detected emitted electronsexclude the backscattered electrons; the detected emitted electrons mayexclude secondary electrons emitted from the pellicle due to aninteraction of the primary electrons with the pellicle and masking thebackscattered electrons.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 illustrates a system, a mask and a pellicle according to anembodiment of the invention;

FIG. 2 illustrates a system, a mask and a pellicle according to anembodiment of the invention;

FIG. 3 illustrates a system, a mask and a pellicle according to anembodiment of the invention;

FIG. 4 illustrates a system, a mask and a pellicle according to anembodiment of the invention;

FIG. 5 illustrates a method according to an embodiment of the invention;and

FIG. 6 illustrates a method according to an embodiment of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Because the illustrated embodiments of the present invention may for themost part, be implemented using electronic components and circuits knownto those skilled in the art, details will not be explained in anygreater extent than that considered necessary as illustrated above, forthe understanding and appreciation of the underlying concepts of thepresent invention and in order not to obfuscate or distract from theteachings of the present invention.

Any reference in the specification to a method should be applied mutatismutandis to a system capable of executing the method and should beapplied mutatis mutandis to a non-transitory computer readable mediumthat stores instructions that once executed by a computer result in theexecution of the method.

Any reference in the specification to a system should be applied mutatismutandis to a method that may be executed by the system and should beapplied mutatis mutandis to a non-transitory computer readable mediumthat stores instructions that may be executed by the system.

Any reference in the specification to a non-transitory computer readablemedium should be applied mutatis mutandis to a system capable ofexecuting the instructions stored in the non-transitory computerreadable medium and should be applied mutatis mutandis to method thatmay be executed by a computer that reads the instructions stored in thenon-transitory computer readable medium.

According to an embodiment of the invention there is provided a methodand system for evaluating a lithography mask such as an extreme ultraviolet (EUV) lithography mask and especially a 16 nanometer EUVlithography mask.

FIG. 1 illustrates a system 41 for evaluating a lithography mask 10according to an embodiment of the invention. FIG. 2 illustrates a system42 for evaluating a lithography mask 10 according to an embodiment ofthe invention. FIG. 3 illustrates a system 43 for evaluating alithography mask 10 according to an embodiment of the invention. FIG. 4illustrates a system 44 for evaluating a lithography mask 10 accordingto an embodiment of the invention.

The lithography mask 10 can be an extreme ultra violet EUV lithographicmask and may be a 16 nanometer EUV lithographic mask. It is illustratedin FIGS. 1-4 as including an upper layer 11, multiple intermediatelayers 12-15 and a substrate (bulk) 16.

System 41 includes:

-   -   a. Electron optics 60 for directing primary electrons 21 towards        a pellicle 30 that is positioned between the electron optics 60        and the lithography mask 10. The primary electrons 21 can be        generated by electron beam source 61 of the electron optics 60.        The primary electrons exhibit an energy level that allows the        primary electrons to pass through the pellicle 30 and to impinge        on the lithographic mask 10. Electron optics 60 may include any        element that can affect the trajectory of the primary electrons        21 as well as their landing energy, or any other        characteristics. The electron optics 60 may include one or more        lenses, one or more apertures, one or more filters, one or more        beam shaping elements, one or more beam splitters, one or more        collimators, one or more deflectors, one or more accelerating        elements, one or more de-accelerating elements, and may include        an electron source. The electron optics 60 may include one or        more detectors such as detector 70.    -   b. Detector 70 for detecting detected emitted electrons and for        generating detection signals indicative of the detected emitted        electrons. The detected emitted electrons are generated as a        result of an impingement of the primary electrons on the        lithographic mask.    -   c. Interface 100 for receiving the detection signals. The        interface 100 may be a communication port, a memory module and        the like.    -   d. Processor 80 for processing the detection signals to provide        information about the lithography mask.

The system can include more than a single detector. The detector 70 canhave multiple separate segments—each arranged to generate detectionsignals reflecting the detected emitted electrons it detected. In FIG. 1the detector 70 is shown as being of an annular shape and four segments71-74 that surround central aperture 76. It is noted that the number,shape and size of detector can differ from those illustrated in FIG. 1.For example, in FIG. 2 the detector 70 has a single annular segment 77that surrounds aperture 76.

The primary electrons 21 form a primary beam that passes through thepellicle 30 and this passage causes the pellicle 30 to emit a firstgroup of emitted secondary electrons SE1 24.

The primary electrons 21 impinge onto the lithographic mask 10 andresult in an emission of backscattered electrons BSE 22.

The backscattered electrons 22 may pass through the pellicle 30 and maycase the pellicle 30 to emit a second group of secondary electrons SE226.

It is noted that the impingement of the primary electrons 21 onto thelithographic mask 10 results in an emission of secondary electrons (notshown) that do not manage to pass through the pellicle 30 and bedetected.

The term “emitted electrons” may refer to the combination ofbackscattered electrons 22, the first group of electrons SE1 24 and thesecond group of electrons SE2 26.

The term “detected emitted electrons” may refer to the part of theemitted electrons that are detected by the at least one detector 70. Forexample, even if the system 41 may be designed to detect emittedelectrons of a certain type (BSE, SE1 and/or SE2) it may occur that onlysome of these certain type of electrons are detected.

Furthermore, according to various embodiments of the invention one ormore types of electrons (outs of SE1, SE2 and BSE) may be masked. Thiscan be implemented by various known masking methods including spatialfilters and energy filters.

System 42 of FIG. 2 differs from system 41 of FIG. 1 by including energyfilters 90 between detector 70 and the pellicle 30. These energy filters90 can be set for masking secondary electrons such as those that belongto the second group of secondary electrons SE2 26.

System 43 of FIG. 3 differs from system 41 of FIG. 1 by having a beamsplitter 110 that is positioned above the pellicle 30 and directsemitted electrons towards detector 70. This arrangement can allow theplane of the pellicle 30 to be imaged onto the detector 70 althoughnon-imaging detection can be applied by system 43. It is noted that theelectron optics 60 may include the beam splitter 110. The electronoptics 60 can include lenses or any other electro-static components(60′) positioned between the beam splitter 110 and detector 70 to focusthe SE electron 24 and 26 on detector 70.

System 44 of FIG. 4 differs from system 41 of FIG. 1 by including a beamsplitter energy 110 positioned above the pellicle 30 and an energyfilter 90 that can be set for masking secondary electrons such as thosethat belong to the first group of secondary electrons SE1 24.

It is noted that the masking can be achieved by the position and shapeof the detector 70. The detector 70 can be positioned and shaped inlocations in which it is expected to detect emitted electrons of onetype and not emitted electrons of another type. For example, thedetector 70 can have (see FIG. 1) a central aperture that allows passageof the primary electrons 21 and also allows a passage of emittedelectrons of the first group of secondary electrons SE1 24 to passthrough without being detected.

FIG. 5 illustrates method 200 according to an embodiment of theinvention.

Method 200 may start by stage 210 of directing by electron optics,primary electrons towards a pellicle that is positioned between theelectron optics and the lithography mask. The primary electrons exhibitan energy level that allows the primary electrons to pass through thepellicle and to impinge on the lithographic mask.

Stage 210 may be followed by stage 220 of detecting, by at least onedetector, detected emitted electrons and generating detection signals.The detected emitted electrons are generated as a result of animpingement of the primary electrons on the lithographic mask.

Stage 220 may include detecting detected emitted electrons that arebackscattered electrons that are emitted from the lithographic mask(detecting BSE). Stage 220 may also include at least one out of (a)masking secondary electrons emitted from the pellicle due to aninteraction of the primary electrons with the pellicle (masking SE1),and (b) masking secondary electrons emitted from the pellicle due to aninteraction of the backscattered electrons with the pellicle (maskingSE2).

The detecting of the detected electrons can be performed by a detectorthat includes multiple backscattered electron detection elements.

Stage 220 may include detecting detected emitted electrons that aresecondary electrons that are emitted from the pellicle due to aninteraction of the backscattered electrons with the pellicle (detectingSE2), wherein the backscattered electrons are emitted from thelithographic mask. Stage 220 may also include at least one out of: (a)masking secondary electrons emitted from the pellicle due to aninteraction of the primary electrons with the pellicle (masking SE1),and (b) masking the backscattered electrons (masking BSE).

Stage 220 may include imaging the plane of the pellicle on the at leastone detector.

Stage 220 may be followed by stage 230 of processing, by a processor,the detection signals to provide information about the lithography mask.The information can be indicative of the state of the lithographic mask,defects of the lithographic mask, shape of the lithographic mask and thelike.

The processing can include any known method or process for extractinginformation from detection signals.

FIG. 6 illustrates method 300 according to an embodiment of theinvention.

Method 300 may start by stage 310 of receiving detection signals. Thedetection signals are generated by at least one detector that detectsdetected emitted electrons. The detected emitted electrons are generatedas a result of directing by electron optics, primary electrons towards apellicle that is positioned between the electron optics and thelithography mask. The primary electrons exhibit an energy level thatallows the primary electrons to pass through the pellicle and to impingeon the lithographic mask.

The detected emitted electrons may include backscattered electrons thatare emitted from the lithographic mask (detecting BSE). The detectedemitted electrons may exclude at least one out of (a) secondaryelectrons emitted from the pellicle due to an interaction of the primaryelectrons with the pellicle (masking SE1), and (b) secondary electronsemitted from the pellicle due to an interaction of the backscatteredelectrons with the pellicle (masking SE2).

The detected emitted electrons may include secondary electrons that areemitted from the pellicle due to an interaction of the backscatteredelectrons with the pellicle (detecting SE2), wherein the backscatteredelectrons are emitted from the lithographic mask. The detected emittedelectrons may exclude at least one out of (a) secondary electronsemitted from the pellicle due to an interaction of the primary electronswith the pellicle (masking SE1), and (b) backscattered electrons(masking BSE).

Stage 310 may be followed by stage 320 of processing, by a processor,the detection signals to provide information about the lithography mask.The information can be indicative of the state of the lithographic mask,defects of the lithographic mask, shape of the lithographic mask and thelike.

The invention may also be implemented in a computer program for runningon a computer system, at least including code portions for performingsteps of a method according to the invention when run on a programmableapparatus, such as a computer system or enabling a programmableapparatus to perform functions of a device or system according to theinvention. The computer program may cause the storage system to allocatedisk drives to disk drive groups.

A computer program is a list of instructions such as a particularapplication program and/or an operating system. The computer program mayfor instance include one or more of: a subroutine, a function, aprocedure, an object method, an object implementation, an executableapplication, an applet, a servlet, a source code, an object code, ashared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer system.

The computer program may be stored internally on a non-transitorycomputer readable medium. All or some of the computer program may beprovided on computer readable media permanently, removably or remotelycoupled to an information processing system. The computer readable mediamay include, for example and without limitation, any number of thefollowing: magnetic storage media including disk and tape storage media;optical storage media such as compact disk media (e.g., CD-ROM, CD-R,etc.) and digital video disk storage media; nonvolatile memory storagemedia including semiconductor-based memory units such as FLASH memory,EEPROM, EPROM, ROM; ferromagnetic digital memories; MRAM; volatilestorage media including registers, buffers or caches, main memory, RAM,etc.

A computer process typically includes an executing (running) program orportion of a program, current program values and state information, andthe resources used by the operating system to manage the execution ofthe process. An operating system (OS) is the software that manages thesharing of the resources of a computer and provides programmers with aninterface used to access those resources. An operating system processessystem data and user input, and responds by allocating and managingtasks and internal system resources as a service to users and programsof the system.

The computer system may for instance include at least one processingunit, associated memory and a number of input/output (I/O) devices. Whenexecuting the computer program, the computer system processesinformation according to the computer program and produces resultantoutput information via I/O devices.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims.

Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under”and the like in the description and in the claims, if any, are used fordescriptive purposes and not necessarily for describing permanentrelative positions. It is understood that the terms so used areinterchangeable under appropriate circumstances such that theembodiments of the invention described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein.

Each signal described herein may be designed as positive or negativelogic. In the case of a negative logic signal, the signal is active lowwhere the logically true state corresponds to a logic level zero. In thecase of a positive logic signal, the signal is active high where thelogically true state corresponds to a logic level one. Note that any ofthe signals described herein may be designed as either negative orpositive logic signals. Therefore, in alternate embodiments, thosesignals described as positive logic signals may be implemented asnegative logic signals, and those signals described as negative logicsignals may be implemented as positive logic signals.

Any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality may be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations merely illustrative. The multipleoperations may be combined into a single operation, a single operationmay be distributed in additional operations and operations may beexecuted at least partially overlapping in time. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

Also for example, in one embodiment, the illustrated examples may beimplemented as circuitry located on a single integrated circuit orwithin a same device. Alternatively, the examples may be implemented asany number of separate integrated circuits or separate devicesinterconnected with each other in a suitable manner.

Also for example, the examples, or portions thereof, may implemented assoft or code representations of physical circuitry or of logicalrepresentations convertible into physical circuitry, such as in ahardware description language of any appropriate type.

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code, such asmainframes, minicomputers, servers, workstations, personal computers,notepads, personal digital assistants, electronic games, automotive andother embedded systems, cell phones and various other wireless devices,commonly denoted in this application as ‘computer systems’.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the terms “a” or “an,” as used herein, are definedas one or more than one. Also, the use of introductory phrases such as“at least one” and “one or more” in the claims should not be construedto imply that the introduction of another claim element by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim element to inventions containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles. Unless statedotherwise, terms such as “first” and “second” are used to arbitrarilydistinguish between the elements such terms describe. Thus, these termsare not necessarily intended to indicate temporal or otherprioritization of such elements. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

We claim:
 1. A method for evaluating a lithography mask, the methodcomprises: directing, by electron optics, primary electrons towards apellicle that is positioned between the electron optics and thelithography mask; wherein the primary electrons exhibit an energy levelthat allows the primary electrons to pass through the pellicle and toimpinge on the lithography mask; detecting, by at least one detector,detected emitted electrons and generating detection signals; whereindetected emitted electrons are backscattered electrons generated as aresult of an impingement of the primary electrons on the lithographymask; masking, by a filter, secondary electrons from detection by the atleast one detector, the secondary electrons emitted from the pellicledue to an interaction of the backscattered electrons with the pellicle;and processing, by a processor, the detection signals to provideinformation about the lithography mask.
 2. The method according to claim1, comprising masking secondary electrons emitted from the pellicle dueto an interaction of the primary electrons with the pellicle.
 3. Themethod according to claim 1, wherein the at least one detector comprisesmultiple backscattered electron detection elements.
 4. A system forevaluating a lithography mask, the system comprises: electron optics fordirecting primary electrons towards a pellicle that is positionedbetween the electron optics and the lithography mask; wherein theprimary electrons exhibit an energy level that allows the primaryelectrons to pass through the pellicle and to impinge on the lithographymask; at least one detector for detecting detected emitted electrons andfor generating detection signals; wherein detected emitted electrons arebackscattered electrons generated as a result of an impingement of theprimary electrons on the lithography mask; at least one mask for maskingsecondary electrons from detection by the at least one detector, whereinthe secondary electrons are generated as a result if impingement of thebackscattered electrons on the pellicle; and a processor for processingthe detection signals to provide information about the lithography mask.5. The system according to claim 4, wherein the system is arranged tomask secondary electrons emitted from the pellicle due to an interactionof the primary electrons with the pellicle.
 6. The system according toclaim 4, wherein the at least one detector comprises multiplebackscattered electron detection elements.
 7. A method for evaluating alithography mask, the method comprises: directing, by electron optics,primary electrons towards a pellicle that is positioned between theelectron optics and the lithography mask; wherein the primary electronsexhibit an energy level that allows the primary electrons to passthrough the pellicle and to impinge on the lithography mask; detecting,by at least one detector, detected emitted electrons and generatingdetection signals; wherein detected emitted electrons are backscatteredelectrons generated as a result of an impingement of the primaryelectrons on the lithography mask; masking, by a filter, secondaryelectrons from detection by the at least one detector, the secondaryelectrons emitted from the pellicle due to an interaction of the primaryelectrons with the pellicle; and processing, by a processor, thedetection signals to provide information about the lithography mask; andmasking secondary electrons emitted from the pellicle due to aninteraction of the backscattered electrons with the pellicle.
 8. Themethod according to claim 7, wherein the at least one detector comprisesmultiple backscattered electron detection elements.